Fiber reinforced composite parts are fabricated utilizing a variety of conventional techniques including resin transfer molding ("RTM"), PREPREG procedures, and preforming operations.
One improvement in RTM is discussed in the applicants, invention entitled "Resin Transfer Molding System and Method" of which this application is a continuation-in-part.
It has been determined that one disadvantage of RTM is that there is a steep learning curve associated with switching to new geometries. Placement of the sprues and vents for resin injection and transfer is not elementary. Therefore, when different geometry parts are to be impregnated by RTM, costly experimentation and analysis is necessary to optimize processing variables and tool design to achieve void free uniform wet out. The analysis required in part stems from the limitation that in conventional RTM operations, resin must travel across the fiber bed.
Another disadvantage is the cost of cleaning the tools associated with RTM. Resin has a tendency to cake on the tools and will ruin the surface finish of the next part to be impregnated if it is not adequately cleaned off the tool surfaces. The biggest disadvantage, however, is the labor intensive and hence costly lay-up of the sheets of dried fiber on a mold surface.
Conventional PREPREG techniques somewhat overcome the void free uniform wetout problems inherent in RTM, but conventional PREPREG techniques require expensive raw materials, costly hand lay-up, and the added equipment cost associated with the autoclave required for curing. And, the autoclave itself adds process variables which must be evaluated as part geometries change.
Certain preforming techniques include utilizing elastomeric sheets which purportedly eliminate the hand lay-up associated with RTM, but as with PREPREG procedures, the raw materials are expensive, and since the preform part must eventually be impregnated, tool cleaning costs as well as the costs associated with void free impregnation are as high as RTM.
Therefore, these methods do not solve the problems of costly hand lay-up, the difficult and complicated analysis required to achieve quality uniform impregnation, and the required cleaning of tools.